The automotive industry, for a number of years, has desired glass having grey color (sometimes called “neutral grey”) for automotive window applications. At the same time, it is also desirable for transmission in the UV (ultraviolet) and/or IR (infrared) ranges of the light spectrum to be minimized. Moreover, certain Governmental regulations in the automotive industry have been known to require that visible light transmittance be at least 70% in certain vehicular windows when provided by the original equipment manufacturer of the vehicle (e.g. GM, Ford, Chrysler etc.) in the U.S.A. While a visible transmittance of 70% or higher is not always required, it is safe to say that high visible transmittance (e.g., 65% or higher) in general is often desired. Accordingly, there exists a need for a glass which achieves high visible transmittance as well as adequate blocking of IR and/or UV rays.
A glass window or other glass article is said to have the desirable color “grey” when it has a dominant wavelength of from 435 nm to 570 nm (this dominant wavelength range defines the color “grey” herein). Moreover, grey glass preferably has an excitation purity (Pe) of less than about 4.5%.
While glass having “grey” color is often desirable, as explained above there sometimes also exists a need or desire to achieve certain levels of light transmission defined conventionally by:                Lta as visible light transmission,        UV as ultraviolet light transmission, and        
IR as infrared light transmission.
Glass thickness ranges of from about 1–6 mm, more preferably from about 3–4 mm, are typically used when measuring the aforesaid characteristics. These thickness ranges are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as recognized thickness ranges in the automotive industry.
Classically formulated grey glasses, such as architectural, often include low levels of iron (i.e., less than 0.4% total iron) along with cobalt and nickel oxides. Unfortunately, while this type of glass may achieve satisfactory coloration in certain instances, it typically suffers from undesirable solar characteristics (e.g., UV and/or IR blockage).
Certain known green solar control float glasses are formulated so as to achieve desirable solar characteristics due in large part to their use of large quantities of total iron (e.g., 0.60 to 0.84% total iron). Unfortunately, the green coloration of such glasses does not always harmonize well with certain exterior automotive paints and sometimes affects vehicle interiors when viewed through the glass, and such large amounts of iron are not always desirable for glass processing.
U.S. Pat. No. 6,235,666 discloses a grey glass composition capable of achieving good solar performance characteristics, including the desirable color grey. In particular, U.S. Pat. No. 6,235,666 discloses a grey glass with a colorant portion including 0.5–0.8% total iron (expressed as Fe2O3), 0.5–3.0% Er2O3, and 0.0–1.0% TiO2. While this is an excellent glass, it is sometimes undesirable in that it requires much of the very expensive erbium oxide (Er2O3). Rather large amounts of total iron (expressed as Fe2O3) are also required in many instances. Thus, there exists a need in the art for a grey glass which can achieve desired grey color in combination with acceptable solar performance properties, without the need for too much total iron and/or erbium.
WO 02/059052 discloses a grey glass including from about 0.35 to 0.5% total iron and from about 0.5 to 1.2% erbium. Again, erbium is very expensive and such large amounts thereof are not always desired. As explained above, there exists a need in the art for a grey glass which can achieve desired grey color in combination with acceptable solar performance properties, without the need for too much erbium.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which overcomes the above problems while achieving one or more of desired grey color and desired solar management property(ies) of the particular industry in which it is to be used.